Method for continuously producing resinoid wheels

ABSTRACT

An abrasive composition prepared by kneading abrasive grains and a binder together, with addition of a filler when desired, is molded into a block, which is heated by a high-frequency wave heater and then passed between multiple pairs of rolls and thereby rolled into a sheet. Circular pieces are blanked out from the rolled sheet and subsequently baked to continuously produce resinoid wheels.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus forcontinuously producing resinoid wheels for cutting hard metal materials.

Conventionally, resinoid bonded grinding wheels have been produced byplacing a kneaded resinoid abrasive composition into a die of a givenshape, smoothing the surface of the composition with raking means togive a uniform thickness to the mass of the composition, molding thecomposition at an elevated pressure and baking the molded product.However, this method has the drawback that relatively coarse abrasivegrains are caught by the raking means and brought to the surface,rendering the resulting product uneven in grain size distribution. Ithas therefore been necessary to prepare abrasive grains of a uniformsize by using a three-stage screening apparatus, but the procedureinvolved is very troublesome and takes a long time. Depending on thescreens employed, moreover, about 10% of oversize grains and fines areseparated off and discarded as being unsuitable for use. Thus theconventional grinding wheels are expensive to make. It is also notedthat even with the use of the three-stage screening apparatus, theselected abrasive grains still have varying sizes, this inevitablyentailing the foregoing drawback. Further according to the conventionalmethod, the raked mass of the starting abrasive composition is pressedon one side for molding, with the result that there arises a differencebetween the pressures acting on the upper and lower surfaces of themolding. When the molding is baked which has been pressed on one sideand is uneven in grain size distribution, the grinding wheel obtainedbecomes uneven in hardness, inasmuch as the product has high hardnesswhere many coarse abrasive grains are present but low hardness wheresmaller grains are predominant. When put to use, the grinding wheelwears away more markedly where it contains many fine abrasive grainsthan where coarse grains predominate, so that an uneven wear takesplace. As a result, the grinding wheel not only fails to cut a workstraight but is also subjected to an objectional force and possiblybroken in an extreme case. Moreover, if the abrasive composition is notfully raked, the resulting product will have a nonuniform thickness,consequently producing errors when cutting a hard metal material, and amarkedly irregular portion of the grinding wheel, if any, will cause anobjectionable force to act on and break the grinding wheel during use.In addition to the many drawbacks of the conventional method describedabove, the aforementioned raking means must operate with very highaccuracy and is therefore expensive and requires a cumbersomemaintenance procedure. The raking procedure is inconvenient in that itmust be followed in a constant temperature and constant humidity chamberso as to render the abrasive composition free of changes in volume.

SUMMARY OF THE INVENTION

This invention provides a method and an apparatus for producing resinoidwheels which have overcome the foregoing problems.

The invention is characterized by a method for producing a resinoidwheel comprising the steps of kneading abrasive grains and a bindertogether, molding the kneaded mixture into a block, heating the moldedblock, rolling the heated block into a sheet, blanking out circularpieces from the sheet and baking the circular pieces.

The invention is further characterized by an apparatus for practicingthe above method to produce a resinoid wheel comprising a kneader forkneading a resinoid abrasive composition, a molding machine for moldingthe kneaded composition into a block, a high-frequency wave heater forthe molded block, a rolling machine for rolling the heated block withmultiple pairs of rolls, a blanking press for blanking out circularpieces from the rolled sheet and means for baking the circular pieces.

According to the present method, a molded block of resinoid abrasivecomposition is efficiently rolled into a sheet of resinoid abrasiveproduct which is tough, free of any distortion and has accuratethickness and good quality. The present method which does not requireany raking means unlike conventional method need not use abrasive grainsof a uniform size, so that the three-stage screening device heretoforeused can be dispensed with, making it unnecessity to discard a portionof the granular abrasive material which will entail a cost increase.Since the block of resinoid abrasive composition is passed betweenmultiple opposing pairs of rotating rolls in succession and is therebyrolled into a sheet, the block is subjected to equal pressures on itsopposite surfaces without permitting any uneven distribution of grainsizes. Whereas it has been entirely infeasible to use abrasive grains offairly different sizes in combination, a resinoid wheel can be producedfrom a mixture of such abrasive grains according to this invention. Infact, the resulting product has a very high cutting ability. Thus thepresent invention eliminates the need for various expensive devices andtroublesome procedures which have conventionally been required and makeit possible to mechanically produce a large quantity of resinoid wheelsat a very low cost. Moreover the resinoid wheels obtained, perfectlyuniform in hardness as well as in thickness, are free of cutting errorsand breakage to assure a uniform and trouble-free operation to cut metalmaterials.

The useful method of this invention can be practiced by the apparatus ofthe invention. It is simple to operate and ensures continuous productionof abrasive wheels having high performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing an embodiment in its entirety ofthe apparatus for producing resinoid wheels according to this invention;

FIG. 2 is a schematic side elevation of the embodiment of FIG. 1;

FIG. 3 is an enlarged view in vertical section showing a block moldingmachine used in this invention;

FIG. 4 is a fragmentary front view of the block molding machine shown inFIG. 3;

FIG. 5 is a side elevation partly broken away and showing a blankingpress used in this invention; and

FIG. 6 is a fragmentary enlarged view in section of the blanking pressshown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2, about 16- to 220-mesh abrasive grainsof silicon carbide, alumina or siliceous sand, a binder such as phenolicresin, epoxy resin, diallyl phthalate resin or like thermosettingsynthetic resin and, when desired, a filler such as creolite, irondisulfide, red iron oxide or clay are fed to two kneaders 1 and 1 inspecified amounts and kneaded together. The proportions by weight ofthese ingredients in the abrasive composition are 60 to 90 parts ofabrasive grains, 10 to 20 part of binder and 0 to 20 parts of filler.The above-mentioned examples of each ingredient may be used singly, orat least two of them are usable conjointly. While the compositioncompletely kneaded in one of the kneaders is being drawn off at aconstant rate from an outlet 2 at its inside lower portion, the startingcomposition is fully kneaded in the other kneader. Scraps of uncuredpre-molded composition resulting from the blanking step are fed to thiskneader at a given rate along with the other ingredients as will bedescribed later. The kneaded composition run off from the kneader 1 issent out by conveyors 3a and 3b to automatic weighing means 4 toautomatically weigh the composition and is thereafter fed to a blockmolding machine 5. The molding machine 5 includes a falt platelike upperdie 20 positioned at its center and movable up and down and two hoxlikelower dies 13 alternately movable outward from the center and theninward. The upper and lower dies 20 and 13 are heated to a temperature,for example, of 70° to 80° C. The resinoid abrasive composition issubjected by the molding machine 5 to pressure, for example, of 80 to140 kg/cm² for 20 to 60 seconds and is thereby molded in succession intoblocks having sizes in the range of from 260 mm × 380 mm × 25 mm to 400mm × 500 mm × 40 mm. The molded block is then heated, for example, to40° to 75° C for 15 to 25 seconds by a high-frequency wave heater 7 andis fed to a rolling machine A including multiple pairs of rolls. Thusthe heated block is fed by a conveyor 8a to rolls 9a for rolling.Usually it is preferable to conduct the rolling operation at leasttwice. The abrasive material is then sent to rolls 9b, 9c and 9d insuccession by conveyors 8b, 8c and 8d. The rolling operation istherefore conducted four times in the illustrated embodiment. By therolling step, the abrasive composition is made into a sheet 400 mm to1,200 mm in width and 1 to 15 mm in thickness. The sheet is then fed byconveyors 8e and 8f to a press 6, by which circular pieces are blankedout from the sheet. In the present embodiment, two to four circularabrasive pieces are blanked from one sheet. The resulting scraps arereturned to the kneaders 1 by way of conveyors 10a, 10b and 10c. Theterminal end 10d of the conveyor 10c is positioned above the kneaders 1and the scraps are supplied to eigher one of the kneaders 1 at a giveninterval. Preferably, infrared projectors are provided above and belowthe conveyors 8b to 8f to prevent the sheet from cooling. The circularpieces obtained are then placed between polished iron discs and baked ona tunnel type electric furnace 56 or like device at a temperaturesuitable for the curing of the aforementioned synthetic resin used asthe binder. For baking, the circular pieces are heated by progressivelyelevating the temperature from room temperature to 180° C over a periodof about one day.

If rolls coated with rubber or some other material equivalent theretosuch as elastic synthetic resin, copper, lead, soft zinc or like softmetal are employed as the terminal pair of rolls for rolling the blockof abrasive composition, the uncured resinoid abrasive piece obtainedcan be made rough-surfaced on its opposite sides. When baked, the piecewill make an improved resinoid wheel.

More specifically, the resinoid bonded grinding wheel thus produced hasrough front and rear surfaces with the abrasive grains alone projectingtherefrom and therefore exhibits a greatly improved cutting ability. Infact, such grinding wheel is capable of cutting steel pipes and likehard metal materials easily, rapidly and with reduced heat generation toproduce a cut surface which is free of burning, distortion anddiscoloration. The resulting cut-off metal piece is accordingly suitablefor the subsequent treatment. In this case the apparatus mayadvantageously include five pairs of rolling rolls, with the terminalpair of rolls covered with rubber, and an additional high-frequency waveheater disposed immediately before the terminal pair to prevent therolled sheet from cooling and to render the sheet rough-surfaced on itsfront and rear sides.

With reference to FIGS. 3 and 4 the block molding machine 5 includessupport columns 11 on the top ends of which an upper plate 12 is placed.Disposed at the center of the machine 5 is a die holder 57, to which isfixed a vertical ram 14. The aforementioned upper die 20 in the form ofa flat plate and provided with a heater 15 is attached to the lower endof the ram 14 and is movable up and down. Mounted on the top plate 12are rails 18 on which are placed two boxlike carriages 16 having wheels17. The lower die 13 in the form of a box having an outwardly projectingflange 19 at its upper end and a loosely fitting bottom 21 is placed oneach of the carriages 16 with shock-absorbing springs 22 interposedtherebetween. The carriages 16 are movable sidewise away from the centerof the molding machine 5 by the operation of hydraulic cylinders 23provided on the opposite sides of the machine 5. The kneaded abrasivecomposition is placed into one of the lower dies 13, which is thenbrought to the center of the machine 5 by the hydraulic cylinder 23,whereupon the upper die 20 is lowered to press and mold the compositionto a block. At this time, the upper die 20 has been heated by a heater15 and, the lower die 13 by a heater 24, to a temperature of 70° to 80°C, at which the abrasive composition is premolded to hardness suitablefor the subsequent rolling operation. In the meantime, the abrasivecomposition is supplied to the other lower die 13. The lower die 13containing the molded composition is retracted sidewise from the centerof the machine 5. Disposed on the opposite sides of and below themolding machine 5 are knockout means 25 having knockout pins 26 whichare movable up and down by vertical hydraulic cylinders 27. When thelower die 13 is retracted sidewise to the position immediately above theknockout means 25, the knockout means 25 functions to force the knockoutpins 26 through the apertures 29 in the bottom plate 28 of the carriage16 to push up the bottom plate 21 of the lower die 13 and to therebyrelease the block from the lower die 13. Simultaneously with this, theother lower die 13 is brought to the center of the molding machine 5,followed by compression molding in the same manner as above. In thisway, the abrasive composition is placed into the two lower dies 13alternately and subjected to compression molding in alternating manner.

The blanking press 6 shown in FIGS. 5 and 6 is formed in its bottomportion with grooves of an inverted U-shaped cross section which fitover guide members 31 on a base frame 30. By the operation of ahydraulic cylinder 40, the blanking press 6 is slidable in one directionalong the uncured rolled sheet of abrasive composition. A releasingagent is applied to the under surface of the rolled sheet to eliminateits tackiness by being passed through means 33 comprising a container 34filled with sand or like releasing agent and two rotary blade wheels 35therein. A photoelectric tube 36 detects the sheet, whereupon theblanking press 6 is initiated into operation. The abrasive sheet 32 issent into a die set 38 by feed rollers 37 and, at the same time, thewhole blanking press 6 slides along on the guide members 31 on the baseframe 30. Simultaneously with this, the upper blade 41 of punch of thedie set 38 descends and comes into contact with the annular movablemember 51 of the die, permitting a lower blade 48 and its holder 49 topush up the movable member 43 of the punch at the same time, whereby acircular abrasive piece is blanked out. The annular upper blade 41 isfixed to the periphery of an upper blade holder 42 which issubstantially in the form of a disc. The circular movable plate 43 hasan upstanding flange 43a and is disposed in a recess in the rear side ofthe upper blade holder 42. Four pins 44 suspended from the upper bladeholder 42 retain the movable plate 43 within the recess, with springs 45and ball slide bearings 47 interposed between the upper blade holder 42and the circular movable plate 43. The annular lower blade 48 is fixedto the periphery of the holder 49 secured to a support frame 50. Theannular movable member 51 for receiving the upper blade 41 is positionedoutside the lower blade and supported by support members 52 on the frame50. springs 54 and ball slide bearings 53 are interposed between themovable member 51 and the support frame 50. When blanking abrasivepieces, compressed air is forced against the under surface of theabrasive sheet from an air outlet 55. The air outlet 55 is provided topermit smooth movement of the abrasive sheet like the aforementionedmeans 33 for applying the releasing agent. Accordingly, one of theoutlet and the applicator means may be used.

The abrasive piece thus blanked out is forced out by the leading end ofthe following advancing abrasive sheet 33 and is drawn out bywithdrawing rollers 39 from the blanking press 6 onto the conveyor 10a,which in turn feeds the piece into baking means 56 in which the piece isbaked by being heated from room temperature to 180° C over a period ofabout 24 hours.

Further in the case where rolls coated with rubber or some other softmaterial are used as the terminal pair of rolls for rolling the moldedblock of the abrasive composition as described previously, the rolledsheet will be rough-surfaced. Therefore, the abrasive grains aloneproject from the front and rear surfaces of the grinding wheel obtained.Consequently, when cutting a metal material, the grinding wheel willcontact therewith over a reduced area, permitting the exposed abrasivegrains alone to contact the metal material to exhibit a greatly improvedcutting ability.

The present invention can be embodied in other different modes withoutdeparting from the spirit and basic features of the invention. Forexample, only one kneader may be employable in place of the two kneadersused in the foregoing embodiment. Thus the embodiment therein disclosedis given for illustrative purposes only and is not limitative in anyway. The scope of this invention is defined by the appended claimsrather than by the above specification. All the modifications andalterations within the scope of the claims are to be construed as beingcovered by the claims.

What is claimed is:
 1. A method for producing a resin-bonded abrasivewheel comprising the steps of:a. kneading abrasive grains having a meshsize in the range of about 16 to 220 mesh, and an uncured thermosettingsynthetic resin binder therefor, in the proportion of about 60 to 90parts by weight of abrasive grains to about 10 to 90 parts by weight ofsaid binder, to form an abrasive composition suitable for molding; b.molding said abrasive composition at a temperature from about 70° toabout 90° C and at a pressure from about 80 to about 140 kg/cm² forabout 20 to 60 seconds, to form a molded block having a thickness of 25to 40 mm.; c. heating said molded block by high frequency wave energyheating at a temperature of about 40° to about 75° C for about 15 toabout 25 seconds; d. rolling said block by multiple pairs of rolls toform a resin-bonded abrasive sheet blank having a thickness of 1 to 15mm.; e. blanking out a circular piece from said sheet; and f. bakingsaid circular piece at a temperature from room temperature to 180° C fora period of 20 to 30 hours to form said wheel.
 2. The method as setforth in claim 1 wherein at least one filler selected from the groupconsisting of creolite, iron disulfide, red iron oxide and clay isfurther incorporated into the abrasive composition by the kneading step.3. The method as set forth in claim 2 wherein the abrasive compositioncomprises 60 to 90 parts by weight of the abrasive grains, 10 to 20parts by weight of the binder and 0 to 20 parts by weight of the filler.4. The method as set forth in claim 1 wherein the block of the abrasivecomposition has a thicknes of 25 to 40 mm and is rolled by multiplepairs of rolls of the rolling step into a sheet having a thickness of 1to 15 mm.
 5. The method as set forth in claim 4 wherein the sheet ofabrasive composition is eventually rough-surfaced on its front and rearsurfaces by the terminal pair of rolls of the rolling step.